1. Field of the Invention
The present invention relates to an inductor structure. More particularly, the present invention relates to an inductor structure having an improved inductor quality.
2. Description of Related Art
Generally speaking, inductors store and release energy through the mutual transformation between electricity and magnetism, so the inductors may be used as a component for stabilizing current. Moreover, in integrated circuits (IC), inductors are very important components but full of challenge. Besides, the inductors have wide applications, for example, in radio frequency (RF) field. In the high frequency field, the inductors are required to have a high quality, i.e., the inductors must have a high quality factor, which is represented by a Q value. The Q value is defined as follows: Q=ω×L/R where ω is the angular frequency, L is the wire inductance, and R is the resistance considering inductance loss under specific frequencies.
In general, various methods and techniques have been proposed for integrating an inductor and an IC process. However, in the IC, the limitation of the thickness of the inductor and the interference of a silicon substrate to the inductor lead to a poor quality of the inductor. In a conventional art, a thick metal is disposed on the top layer of the inductor, so as to reduce the conductor loss, and raise the Q value of the inductor.
However, although having a thick metal at the top layer, the inductor structure may still be influenced by an eddy current. As the inner coil turn has the maximum magnetic flux, the inner portion of the inner coil turn is most affected by the eddy current. Thus, the current of the inner coil turn is not uniform, and the cross-sectional area of the conductor cannot be fully utilized, which reduces the inductor quality.